1. Field of the Invention
The present invention relates to a magnetostrictive transducer that generates an elastic ultrasound wave in a plate member or measures the same and an apparatus of monitoring structural health using the magnetostrictive transducer, and more particularly, to a magnetostrictive transducer that generates a large shear horizontal (SH) wave by using magnetostriction, and an apparatus and method for monitoring structural health by using the magnetostrictive transducer.
The present invention is derived from a research project sponsored by the Korea Science and Engineering Foundation and Seoul National University R&DB Foundation.
[2009-0083279, Multi-Scale Paradigm for Creative Design of Multi-Physical Complex Structure System].
2. Description of the Related Art
Magnetostriction refers to mechanical deformation of ferromagnetic materials when the ferromagnetic materials are in a magnetic field. It is also referred as Joule effect. An inverse effect thereof is referred as an inverse magnetostrictive effect or Villari effect in which a magnetic state of a material changes when stress is applied thereto.
A magnetostrictive transducer may be used to measure deformation of an object without mechanically contacting the object, and is thus widely employed in various fields where contact type sensors cannot be used. When using magnetostriction, an elastic wave may be generated contactlessly, and furthermore, a larger elastic guided wave may be generated compared to the case when using the conventional piezoelectric effect.
In general, a guided wave in a thin plate member is classified as a Lamb wave or a shear horizontal (SH) wave according to a vibration method of particles. The SH wave refers to an elastic wave along which particles vibrate perpendicularly in a propagating direction of the wave through a horizontal plane of a plate member. In particular, in a first mode of the SH wave, the SH wave propagates without colliding with an upper or lower boundary, and thus there is no particle dispersion and the SH wave can be transmitted with high efficiency. Thus, the SH wave may be effectively used in non-destructive testing of the plate member.
FIGS. 1 and 2 schematically illustrate deformation of a ferromagnetic material due to magnetostriction.
Referring to FIG. 1, when a first magnetic field BS and a second magnetic field BD are applied perpendicularly to each other in the vicinity of a magnetic deformation body 1, the magnetic deformation body 1 may be deformed in a shearing direction as illustrated in FIG. 2. That is, the first magnetic field BS is a static magnetic field, which remains constant without any variation in the intensity thereof, and the second magnetic field BD is a dynamic magnetic field. Thus, the magnetic deformation body 1 is deformed according to the variation in the magnetic field of the second magnetic field BD as illustrated in FIG. 2.
According to the conventional art, it is difficult to generate a large SH wave in a plate member. A small SH wave may be generated in a plate member, but a width thereof is small and the SH wave is transmitted almost linearly only in a predetermined direction. Thus, a small SH wave is not useful for monitoring a defect position in a plate member over a large area. In addition, it is difficult to adjust a frequency at which the SH wave is generated.